The present invention relates to a device for protecting a fuel tank made of synthetic resin from heat of a muffler and an exhaust pipe in an exhaust system of an automotive engine and from fire on roads.
Plastic fuel tanks are generally manufactured by blow molding. Therefore, as shown in FIG. 4, a fuel tank 1 has a pinch-off portion 3 on a side wall 2 of the fuel tank 1 at a juncture thereof.
Such a plastic fuel tank is easily deformed by fire and heat. Japanese Patent Laid Open 57-140226 discloses a fuel tank, a body of which is covered with heatproof material to improve its heatproof and fireproof characteristics. In accordance with another means for protecting the tank from heat, a part of the exhaust system such as a muffler is covered with a plate for intercepting the heat.
For example, in a device shown in FIG. 5, a muffler 4 is disposed under a car body adjacent a fuel tank 1. A heat cutoff plate 5 encloses a main part of the muffler 4 to prevent the heat of the muffler from affecting the tank 1.
However, the heat cutoff plate acts to intercept only the heat of the exhaust system. Accordingly, when a fire breaks out in the exhaust system as a result of overheating, or breaks out on the road, the cutoff plate can not prevent the tank from the flames, so that the flames touch the side walls of the tank 1 as shown by arrows in FIG. 5. The flames heat the walls of the tank, thereby breaking a part of the walls, especially the pinch-off portion. Further, the side walls above the level of the fuel in the tank such as gasoline is heated earlier than the lower portions of the side walls, because the inside of the upper side walls which is above the level of the fuel does not contact the fuel. Accordingly, a part of the side walls of the lower portion adjacent the pinch-off is stretched by the weight of the fuel and the tank. Thus, this part gradually thins out, resulting in breaking of the part.
In order to prevent such trouble, a fuel tank having a thick wall is used or a heat cutoff plate is provided to completely cover the underside of the tank. However, such measures increase the manufacturing costs. Moreover, water enters into the space between the heat cutoff plate and the fuel tank, which will cause corrosion of the heat cutoff plate.